Variable coaxial attenuator

ABSTRACT

A variable coaxial attenuator comprising a conductive casing having first input means and first output means for connecting the casing to the outer conductor of a coaxial transmission line, an inner conductive member disposed in the casing and spaced from the walls of the casing, second input means and second output means for connecting the inner conductor of a coaxial transmission line to the inner conductive member, lossy dielectric material disposed in the walls of the casing, and a pair of conductive plate members movably supported for movement between a nonobstructing position in which the lossy dielectric material will be entirely in the field of electromagnetic energy carried by the coaxial transmission line and an obstructing position in which the conductive plate members are disposed between the inner conductive member and the lossy dielectric material so that none of the electromagnetic energy carried by the coaxial transmission line is absorbed by the lossy dielectric material.

United States Patent [72] lnventor Ronald Davo Succasunna, NJ. [21] AppLNo. 19,908 [22] Filed Mar. 16,1970 [45] Patented Dec.2l,l97l [73] Assignee Meca Electronics, Inc.

Denville, NJ.

[54] VARIABLE COAXIAL ATTENUATOR 12 Claims, 4 Drawing Figs.

[52] U.S.Cl 333/81 A, 333/9712 [51] 1nt.Cl l-lillp 1/22 [50] FieldoiSearch 333/81,22, 97;338/216 [56] References Cited UNITED STATES PATENTS 2,842,748 7/1958 Vallese 333/81 2,877,434 3/1959 Farretal... 333/98 3,215,958 1l/1965 lsaacson.... 333/81 3,218,583 11/1965 Ponetal..... 333/81 Assistant Examiner-Marvin Nussbaum Att0rneyLerner, David 81. Littenberg ABSTRACT: A variable coaxial attenuator comprising a conductive casing having first input means and first output means for connecting the casing to the outer conductor of a coaxial transmission line, an inner conductive member disposed in the casing and spaced from the walls of the casing, second input means and second output means for connecting the inner conductor of a coaxial transmission line to the inner conductive member, lossy dielectric material disposed in the walls of the casing, and a pair of conductive plate members movably supported for movement between a nonobstructing position in which the lossy dielectric material will be entirely in the field of electromagnetic energy carried by the coaxial transmission line and an obstructing position in which the conductive plate members are disposed between the inner conductive member and the lossy dielectric material so that none of the electromagnetic energy carried by the coaxial transmission line is absorbed by the lossy dielectric material.

This invention relates to coaxial transmission line components, and particularly to a variable coaxial transmission line attenuator.

Coaxial transmission line attenuators are used to reduce the amplitude of signals, such as microwave signals, carried by a coaxial transmission line. It is often desirable to utilize a variable attenuator where the amount of reduction of the amplitude of the signals, or power dissipation, can be varied from, for example, zero to a desired maximum attenuation. Such variable attenuation must be effected while maintaining a good impedance match between the connected coaxial transmission line segments and/or, for example, microwave circuit components.

There are presently available many devices and/or methods of providing for variable coaxial transmission line attenuators including, for example, the use of variable resistances, the use of a variable power divider for shunting varying amounts of power to a dummy load, and the use of a lossy dielectric material which can be moved partially or fully into the electromagnetic field of a coaxial transmission line. The present invention is directed to devices employing the latter method.

Present variable coaxial transmission line attenuators employing lossy dielectric materials generally provide means for moving the lossy dielectric material into and out of the electromagnetic field of a coaxial transmission line. The more lossy dielectric material disposed in the electromagnetic field, the greater the attenuation. It has not been feasible to date to employ such devices when large amounts of energy are to be dissipated, such as when working with high-power transmissions. This is due to the fact that when the electromagnetic energy is absorbed by the lossy dielectric material, the energy is converted to heat which raises the temperature of the lossy dielectric material. Because the lossy dielectric material is movably mounted, it is difficult to provide effective means for removing large amounts of heat from the lossy dielectric material since, for example, it cannot be in intimate contact with the attenuator housing and an air gap, though quite small, is created which inhibits efiicient flow of heat from the lossy material to the attenuator housing.

It is the general object ofthis invention to provide a new and improved variable coaxial attenuator which employs lossy dielectric material, and particularly such an attenuator with high-power dissipation capability.

SUMMARY OF THE INVENTION According to the present invention, there is provided a variable coaxial attenuator comprising a conductive casing having first input means and first output means for connecting the casing to the outer conductor of a coaxial transmission line, an inner conductive member disposed in the casing and spaced from the walls of the casing, second input means and second output means for connecting the inner conductor of a coaxial transmission line to the inner conductive member, lossy dielectric material disposed in the walls of the casing, and a pair of conductive plate members movably supported for movement between a nonobstructing position in which the lossy dielectric material will be entirely in the field of electromagnetic energy carried by the coaxial transmission line and an obstructing position in which the conductive plate members are disposed between the inner conductive member and the lossy dielectric material so that none of the electromagnetic energy carried by the coaxial transmission line is absorbed by the lossy dielectric material.

It is to be noted that contrary to present practice, movable lossy dielectric members are not employed. Instead, movable conductive shield members are utilized. Further, the lossy dielectric material is disposed in the walls of the conductive casing thereby providing a very efiective means of removing heat from the lossy dielectric material.

In accordance with a further feature of the invention, the lossy dielectric material is disposed in separate layers one in each of a pair of sidewalls. Further, each of the layers has tapered end portions which effect :a desired distribution of electromagnetic energy absorption as well as uniform heat distribution of the heat produced.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be fully understood, it will now be described with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a known variable coaxial attenuator;

FIG. 2 is a cross-sectional view taken along lines 1-] of FIG.

FIG. 3 is a crosssectional view of an attenuator according to the present invention; and

FIG. 4 is a cross-sectional view of the attenuator of FIG. 3 taken along lines Il-lI.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is believed that the present invention may be more easily and fully appreciated by one who is familiar with the presently known closest state of the art. To this end, FIGS. 1 and 2 illustrate a conventional coaxial attenuator which uses lossy dielectric material for effecting power dissipation. In the following description, like reference numerals will be used throughout to refer to similar parts.

Referring now to FIGS. 1 and 2, the known variable coaxial attenuator 10 comprises a conductive casing 12. Casing 12 is made up of a plurality of metal walls including top and bottom wall members 15 and 16, end wall members 16 and 18, and sidewall members 20 and 22.

Outer conductive coupling members are fixedly attached to the end walls 16 and 18 for connection to the outer conductor of a coaxial transmission line. The outer conductive coupling members consist of a first coupling member 24 attached to end wall 16 and a second coupling member 26 attached to end wall 18. Dielectric spacer support members 28 and 30 fixedly support the tapered ends 32 and 34 of an inner conductive member 36 within and coaxially with couplings 24 and 26 respectively. A central generally planar conductive portion 38 connects the ends 32 and 34 together. The tapered ends or end portions 32 and 34 are a standard means of impedance matching a transition from round to flat conductors.

A pair of tapered slabs 40 and 42 of lossy dielectric material are fixedly supported by screw shaft 44. The shaft 44 is part of an adjustable support assembly 46 which is generally sche matically illustrated. It will be appreciated that such support means are well known and provide means for moving the slabs 40 and 42 from a position in which they are disposed on either side of conductive portion 38 and fully within the electromagnetic field created by current flowing through the conductive member 36 to provide for maximum attenuation to a position above conductive portion 38 out of the electromagnetic field created by the current flowing through inner conductive member 36 to provide for minimum attenuation. Completely variable attenuation is provided since the slabs can be moved from the nonobstructing position at their maximum height within the casing, in which the lossy dielectric material ofslabs 40 and 42 will not be within the electromagnetic field surrounding conductive portion 33 down to the bottommost fully obstructing position in which the lossy dielectric material will be fully within the electromagnetic [field surrounding the center conductor, and vice versa. Further, the slabs 40 and 42 can be positioned at any position between the fully nonobstructing and fully obstructing positions.

Slabs 40 and 42 cannot be affixed to the sidewalls 20 and 22 of casing 12 without prohibiting movement of the slabs which is necessary to provide for the desired capability of varying the attenuation effected by attenuator 10. Therefore, even if the slabs 40 and 42 are in sliding contact with the sidewalls 20 and 22, there will be some gap between the slabs andthe sidewalls which will inhibit efficient heat transfer from the slabs to the metal sidewalls.

The present invention will now be described with reference to FIGS. 3 and 4 in which a variable coaxial attenuator 50 made in accordance with the teachings of the present invention is shown. Coaxial attenuator 50 differs from the conventional coaxial attenuator in that conductive shielding means 52 are movably supported by shaft 44 and layers of lossy dielectric material 54 and 56 are disposed in sidewalls 58 and 60. Thus, the layers of lossy dielectric material 54 and 56 are in intimate contact with the metal sidewalls 58 and 60 to provide for efficient heat transfer therebetween.

The conductive shielding means 52 comprises a pair of spaced parallel plate members 62 and 64. In preferred embodiment, the plate members are made of metal. Maximum attenuation is effected when the plate members 62 and 64 are in their uppermost position thereby fully exposing the layers of lossy dielectric material 54 and.56 to the electromagnetic field surrounding conductive portion 38. Minimum attenuation is effected when the metal plates 62 and 64 are in their bottommost positions shielding the electromagnetic field from the layers of lossy dielectric material 54 and 56. in this regard, the spacing between the metal plates and the center conductor is chosen to provide a perfect impedance match when the plates are in their bottommost position. in this position, none of the electromagnetic energy will be absorbed by the layers of lossy dielectric material 54 and 56.

it will be appreciated that any position between the topmost and bottommost position can be selected by manipulation of the support means 46. The greater the area of exposure of the lossy dielectric material to the electromagnetic field surround center conductive portion 38, the greater the amount of electromagnetic energy absorbed by the dielectric material with resultant increased attenuation of the signal.

A great variety of lossy dielectric materials are well known to those skilled in the present art. The selection of the desired lossy dielectric material depends upon the desired performance parameters such as attenuation per unit length, attenuation proportional to frequency, resistance to heat, machineability, moldability, etc. Also, the particular support means and method of adjusting the position of the conductive shielding means 52 would depend on the desired manner of operation. Further, many means can be provided for securing the slabs of lossy dielectric material 54 and 56 to the metal sidewalls 58 and 60. For example, molding or cementing with heat-conducting cement, the use of heat-conductive fasteners, the use of a thin coat of heat-conductive paste in combination with metal fasteners, etc. in fact, it may well be that instead of disposing the lossy dielectric material directly in the walls of the casing, it could be connected to the casing or a heat sink by suitable heat-conducting means which can be easily effected in accordance with the present invention since the lossy dielectric material need not be movable.

Referring again to FIGS. 1 and 2, the slabs 40 and 42 of lossy dielectric material are tapered to provide a desired uniform energy absorption characteristic. in like manner, the layers of lossy dielectric material 54 and 56 shown in FIGS. 3 and 4 are tapered to provide for uniform electromagnetic energy absorption as well as uniform heat dissipation through the sidewalls 58 and 60. It will be appreciated that shapes other than the illustrated one may be used as long as the effect is to provide the desired distribution of electromagnetic energy absorption and/or heat distribution.

While the principles of the invention have been described in connection with a specific embodiment thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention as set forth in the accompanying claims.

What is claimed is:

1. In a variable coaxial transmission line attenuator comprising:

a. a conductive casing;

b. first input means adapted to connect said casing to the outer conductor ofti coaxial transmission line;

c. first output means adapted to connect said casing to the outer conductor of a coaxial transmission line;

d. second input means adapted to be connected to the inner conductor of a coaxial transmission line;

e. second output means adapted to be connected to the inner conductor of a coaxial transmission line;

an inner conductive member disposed in said casing and connecting said second input means to said second output means; and

g. electromagnetic energy absorption means disposed in said casing;

the improvement that h. conductive means capable of establishing a conductive shield between said inner conductive member and said electromagnetic energy absorption means is disposed in said casing; and,

. adjustable support means movably support said conductive means for movement to a desired position between a first nonobstructing position in which the maximum amount of electromagnetic energy carried by the coaxial transmission line will be absorbed by the electromagnetic energy absorption means and a second obstructing position in which the said conductive means is approximately fully disposed between the inner conductive member and the energy absorption means so that a minimum amount of the electromagnetic energy carried by the coaxial transmission line will be absorbed by the electromagnetic energy absorption means.

2. An attenuator according to claim 1, wherein said casing comprises a pair of oppositely disposed sidewalls, and said electromagnetic absorption means comprises a layer of lossy dielectric material disposed in each of said sidewalls.

3. An attenuator according to claim 2, wherein said inner conductive member comprises an elongated generally planar member disposed generally centrally of and generally parallel to said sidewalls, said conductive means comprises a pair of spaced, generally parallel conductive plate members, and said support means supports said spaced plate members generally in parallel with said elongated generally planar member for movement in parallel paths from said first nonobstructing position to said second obstruction position in which said spaced plate members are disposed on opposite sides of said elongated planar member.

4. An attenuator according to claim 2, wherein said layers of lossy dielectric material are shaped to provide a desired distribution of electromagnetic energy absorption.

5. An attenuator according to claim 4, wherein each of said layers of lossy dielectric material has a generally uniform depth, a central portion having a generally uniform width, and uniformly tapered end portions which taper from the central portion.

6. An attenuator according to claim 3, wherein said layers of lossy dielectric material are shaped to provide a desired dis tribution of electromagnetic energy absorption.

7. An attenuator according to claim 6, wherein each of said layers of lossy dielectric material has a generally uniform depth, a central portion having a generally uniform width, and uniformly tapered end portions which taper from the central portion.

8. A variable coaxial attenuator comprising a conductive casing, first input means and first output means for conductively connecting said casing to the outer conductor of a coaxial transmission line, an inner conductive member disposed in said casing and spaced from the walls thereof, second input means and second output means for connecting the inner conductor of a coaxial transmission line to said inner conductive member, lossy dielectric material members disposed in said casing, a pair of conductive plate members, and support means movably supporting said plate members for movement between a nonobstructing position in which said lossy dielectric material members will be entirely in the field of elecof lossy dielectric material are shaped to provide a desired distribution of electromagnetic energy absorption.

11. An attenuator according to claim 8, wherein said casing comprises a pair of oppositely disposed sidewalls, and said electromagnetic absorption means comprises a layer of lossy dielectric material disposed in each of said sidewalls 12. An attenuator according to claim I. wherein said electromagnetic energy absorption means are fixedly connected to said casing. 

1. In a variable coaxial transmission line attenuator comprising: a. a conductive casing; b. first input means adapted to connect said casing to the outer conductor of a coaxial transmission line; c. first output means adapted to connect said casing to the outer conductor of a coaxial transmission line; d. second input means adapted to be connected to the inner conductor of a coaxial transmission line; e. second output means adapted to be connected to the inner conductor of a coaxial transmission line; f. an inner conductive member disposed in said casing and connecting said second input means to said second output means; and g. electromagnetic energy absorption means disposed in said casing; the improvement that h. conductive means capable of establishing a conductive shield between said inner conductive member and said electromagnetic energy absorption means is disposed in said casing; and, i. adjustable support means movably support said conductive means for movement to a desired position between a first nonobstructing position in which the maximum amount of electromagnetic energy carried by the coaxial transmission line will be absorbed by the electromagnetic energy absorption means and a second obstructing position in which the said conductive means is approximately fully disposed between the inner conductive member and the energy absorption means so that a minimum amount of the electromagnetic energy carried by the coaxial transmission line will be absorbed by the electromagnetic energy absorption means.
 2. An attenuator according to claim 1, wherein said casing comprises a pair of oppositely disposed sidewalls, and said electromagnetic absorption means comprises a layer of lossy dielectric material disposed in each of said sidewalls.
 3. An attenuator according to claim 2, wherein said inner conductive member comprises an elongated generally planar member disposed generally centrally of and generally parallel to said sidewalls, said conductive means comprises a pair of spaced, generally parallel conductive plate members, and said support means supports said spaced plate members generally in parallel with said elongated generally planar member for movement in parallel paths from said first nonobstructing position to said second obstruction position in which said spaced plate members are disposed on opposite sides of said elongated planar member.
 4. An attenuator according to claim 2, wherein said laYers of lossy dielectric material are shaped to provide a desired distribution of electromagnetic energy absorption.
 5. An attenuator according to claim 4, wherein each of said layers of lossy dielectric material has a generally uniform depth, a central portion having a generally uniform width, and uniformly tapered end portions which taper from the central portion.
 6. An attenuator according to claim 3, wherein said layers of lossy dielectric material are shaped to provide a desired distribution of electromagnetic energy absorption.
 7. An attenuator according to claim 6, wherein each of said layers of lossy dielectric material has a generally uniform depth, a central portion having a generally uniform width, and uniformly tapered end portions which taper from the central portion.
 8. A variable coaxial attenuator comprising a conductive casing, first input means and first output means for conductively connecting said casing to the outer conductor of a coaxial transmission line, an inner conductive member disposed in said casing and spaced from the walls thereof, second input means and second output means for connecting the inner conductor of a coaxial transmission line to said inner conductive member, lossy dielectric material members disposed in said casing, a pair of conductive plate members, and support means movably supporting said plate members for movement between a nonobstructing position in which said lossy dielectric material members will be entirely in the field of electromagnetic energy carried by a connected coaxial transmission line and an obstructing position in which the plate members are disposed between said inner conductive member and said lossy dielectric material members to prevent absorption of electromagnetic energy by said lossy dielectric material members.
 9. An attenuator according to claim 8, wherein said lossy dielectric material members comprises layers of lossy dielectric material disposed in and fixedly conductively connected to at least two portions of the walls of said casing.
 10. An attenuator according to claim 9, wherein said layers of lossy dielectric material are shaped to provide a desired distribution of electromagnetic energy absorption.
 11. An attenuator according to claim 8, wherein said casing comprises a pair of oppositely disposed sidewalls, and said electromagnetic absorption means comprises a layer of lossy dielectric material disposed in each of said sidewalls.
 12. An attenuator according to claim 1, wherein said electromagnetic energy absorption means are fixedly connected to said casing. 